<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="utf-8">
        <style>
        * {
            padding:0;
            margin:0;
        }
            div {
                width:100px;
                height:100px;
                background-color:cyan;
            }
        </style>
    </head>
    <body>
    <div></div>
    </body>
</html>